Introduction: During the thirty years ago noise pollution increased quickly in the urbane communities that motorcycles are chief sources of noise. The objective of this study is reduction of noise emitted from motorcycle exhaust, applying engineering design.
Materials and Methods: In this pre-experimental study, current condition of noise emitted from motorcycle exhaust and physical parameters of exhaust gas is determined and measured again after planning. In this study JIS D 1616 and SAE J1287 are used for noise measurement and JIS B 8006 and JIS B 8007 respectively for pressure and temperature measurement of exhausted gas from Honda CG125 type of motorcycle. For noise, temperature and pressure measurement of exhausted gas, cell 490 sound level meters, ordinary mercury thermometer, pitot tube and inclined manometer were used respectively.
Results: In this motorcycle, in the natural rpm (3000 rpm), Noise level emitted from current silencer was 97.74 dBC and in type 2 reduced to 94.54 dBc. In the natural rpm (3000 rpm) insertion loss of current silencer in 100-400 HZ was equal to 10.94 dB and by engineering planning this parameter reached to 14.22 dB.
Conclusion: For reduction of noise emitted from motorcycle exhaust it is better to use reflective and simple silencer
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